During the course of the past several years, substantial effort has been devoted to developing more environmentally friendly alternatives to materials which had previously been frequently used for refrigeration and air conditioning purposes. During this time, the main refrigerant used for mobile air conditioning (MAC) systems had been HFC-134a. Although HFC-134a possesses many properties that make it attractive for use in MAC systems, it has a relatively high global warming potential (GWP) of about 1430 (100 years).
The fluorinated olefin HFO-1234yf has emerged after much research and development effort by the assignee of the present invention as the material of choice to replace HFC-134a in MAC systems. The emergence of HFO-1234yf as the next-generation material of choice for MAC systems is due primarily to its exceptional ability to provide a combination of difficult to achieve properties, such as excellent heat transfer characteristics, low toxicity, low flammability, and chemical stability, among other properties. Furthermore, HFO-1234yf is capable of providing this combination of properties with little or no need to be blended with other materials.
Despite the exceptional and extraordinary success of HFO-1234yf as the next generation refrigerant for many applications, including particularly MAC systems, the present applicants have come to appreciate that circumstances may arise in which HFO-1234yf is not readily available as a result of production capacity limitations, especially in the near term. Accordingly, applicants have come to recognize the need for the development of other materials which might approach the commercial success of HFO-1234yf as the next generation refrigerant.
Prior to and subsequent to the development of HFO-1234yf, much of the effort directed toward next-generation refrigerants was focused on the development of heat transfer compositions comprised of a blend or mixture of two or more components. However, these efforts have thus far been generally less than fully successful because of a failure to fully realize one or more of the myriad of properties required for a successful next generation refrigerant.
The fluorinated olefin 1,3,3,3-tetrafluoropropene (HFO-1234ze) has also been identified in an application assigned to the assignee of the present invention as a next generation refrigerant due to its advantageous combination of properties. See, for example, WO 2009/089511. While this application discloses that HFO-1234ze is very attractive as a refrigerant in many applications, it also reveals that it has a substantially lower capacity relative to HFC-134a than does HFO-1234yf in certain air conditioning applications when each is used as the sole refrigerant.
Blends comprising such fluorinated olefins (e.g. 1234ze or 1234yf) have been suggested for use in a wide variety of applications, including heat transfer compositions. For example, WO 2009/089511, discloses blends comprising as a first component one or more fluorinated olefins according to a particular structure and a second component selected from a list of compounds comprising chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) water and CO2. However, the specific combination of components in the particular concentration ranges required by the present invention are not disclosed, and no particular combination of these components is identified in WO 2009/089511 as having the advantageous and beneficial properties described herein.
US Application No. 2010/0044619, which is also assigned to the assignee of the present invention, discloses blends comprising fluorinated olefins for use in connection with heat transfer compositions. This application describes blends comprising as a first component dichloromethane (HFC-32), second component comprising multi-fluorinated olefins having from 2 to 5 carbon atoms, and optionally a third component selected from fluorinated alkanes having to 2 to 3 carbon atoms, CF3I, and combinations of these. According to this application, the second and/or third component of the blend is incorporated for the purpose of acting as of an agent for reducing the flammability of the material relative to HFC-32 alone. Once again, however, the specific combination of components in the particular concentration ranges required by the present invention are not disclosed, and no particular combination of these components is identified in US Application No. 2010/0044619 as having the advantageous and beneficial properties described herein.
Although it is believed that the blends of materials disclosed in the above-noted applications are generally acceptable for use in heat transfer applications under certain circumstances, applicants have found that unexpected yet highly beneficial advantages can be achieved by careful selection of materials within a specific concentration range for forming a heat transfer composition blend which is at once capable of achieving highly desirable heat transfer properties, extraordinarily beneficial environmental properties and exceptionally and unexpectedly nonhazardous compositions from the standpoint of combustion ignition.
The burning velocity of a material is one measure that has heretofore been used to assess the hazardousness of the material from a flammability or explosive nature stand point. Thus it has heretofore been considered in many applications that a material having a burning velocity below a value of 10 (measured as described hereinafter), is not only important or essential for many applications, but also that such a material would be considered generally a non-hazardous material from a flammability or explosive nature stand point. Applicants have found that certain compositions exhibit an undesirably high level of hazardousness even when such compositions contain components that would indicate that the material is acceptable for use from a burning velocity stand-point, as discussed more fully hereinafter.